The primary specific aim of the OHTS II cohort study is to determine if there is a penalty for delaying treatment in ocular hypertension. The primary specific aim will be tested by comparing the long-term cumulative incidence of POAG and adverse events in the original observation participants in OHTS I who start treatment in OHTS II to the long-term cumulative incidence in medication participants who received medication throughout OHTS I and who continue treatment in OHTS II (Primary Specific Aim). The specific aim of the Coordinating Center is to provide overall scientific leadership and operational support to accomplish the primary and secondary specific aims of OHTS II by: 1. Developing, distributing and maintaining a detailed Manual of Procedures 2. Training and certifying clinical staff in OHTS II study protocol and procedures 3. Monitoring adherence to the OHTS II protocol and providing feedback to clinic staff and resource centers 4. Ensuring collaboration between clinics and resource centers 5. Monitoring efficacy and safety at semi-annual intervals and as requested by the Data and Safety Monitoring Committee 6. Receiving, editing, storing and analyzing data from participating clinics, Visual Field Reading Center, Optic Disc Reading Center, Confocal Scanning Laser Ophthalmoscope Reading Center and the Short Wave Length Perimetry Reading Center. 7. Providing methodological and statistical expertise in the preparation of presentations and publications 8. Developing plans for the orderly close-out of the study including participants, clinics, and resource centers 9. Archiving and documenting study data.